Abstract: :
Purpose: Exposure to light greatly influences the progressionof degeneration in the T4R RHO dog. To better understand therole of light in the degenerative process, we used immunocytochemicaland apoptotic markers to characterize changes that occur atspecific time points following focal or full field light exposure.Methods: Age matched, dark adapted T4R+/– and wt dogswere exposed to either focal (3mm diameter) or full field illuminationusing light levels comparable to those used in clinical fundusphotography, and enucleated at selected time points followingexposure. Eyes were fixed in paraformaldehyde, embedded in OCT,and sectioned for immunocytochemistry and TUNEL staining.Results:Apoptotic changes, including positive TUNEL staining,were noted within 2 hours of light exposure. Immunocytochemicalchanges of constituent retinal and RPE proteins, including rhodopsin,cone opsins, arrestin and RPE65, were also found. At 2 and 24hrs following exposure, there was shortening, fragmentationand disorganization of outer segments; RPE cells became reactive,proliferated and migrated into the subretinal space. These changeswere found exclusively in light exposed areas of the retina.Conclusions: Exposure to light levels like those used in clinicalretinal examinations modifies the progression of retinal degenerationin the RHO T4R mutant dog. Dogs with this mutation provide animportant large animal model to examine the interactions ofmutation and environment in determining the severity of theretinal disease phenotype.